Double-screw jack



March 2 1926.

A. L. JOHNSON ET AL DOUBLE SCREW JACK Filed April a, 1925 changing from one motion to the other, no change in the rapidity of motion, no spring pawl or the like to operate or possibly get out of order, and in fact, the ordinary operator will not know that any change is talring place except that it begins to turn harder. The same is true on the downward motion. The inner screw is operated directly by the gear to rise without operating the outer screw. rIhis direct operation is a simplification and reduces the friction.

ln the use ot the device, it is desirable to set the jack before it is put under the car so that it will be of approximately the right height and this can be done by holding it by the guide Q2 and turning the base l0. lt will be'seen that it, 'for any reason, the thread of the inner screw does not turn easily in the outer screw, on account ot there being more resistance there than on the outer thread, still the jack will operate all right as it makes no difference whether both screws go up at once during the irst part of the operation or later. In other words, the etliciency of the jack is not lost it the inner screw shouldV bind. rl`his, however, is not likely to happen.

Although we have illustrated and described only a single torni ot the invention, we are aware of the fact that modilications can be made therein by any person skilled in the art without departing from the scope oi the invention as expressed in the claims. Therefore we' do not wish to be limited to all the details of construction herein shown and described but what we do claim is:-

l. In a jack of the character described, the combination of an operating gear having a passage therethrough, an inner screw located in said passage and movable vertically therethrough, means whereby the inner screw is caused to rotate positively with the gear, a nut below the gear orthe inner screw to cause it to rise or descend as it rotates, and means whereby said nut will rise or descend with the rotation of the gear after the inner screw has reached the limit of its travel.

2. In a jack, the combination with astandard screw-threaded internally, ot' a screw operating in said screw thread and having a passage therethrough also threaded, an inner screw threaded in said passage and having a. longitudinal key-way, a gear rotatably mounted at the top of the standard aud having a passage therethrough tor the inner screw and a projection for engagingv the keyway, means 'for operating the gear, and means at the bottom of the inner screw ttor engaging the bottom of the inner thread on Vthe outer screw when the inner screw rises to its limiting position, whereby from that time on the outer screw and inner screw will turn together and both rise in accordance with the thread on the outside of the outer screw.

3. In a jack, the combination ot a standard having a vertical passage therethrough with an internal thread extending for a distance therealong, a hollow screw mounted in said thread and having an internal thread extending for a shorter distance therealong, an inner screw mounted in the second internal thread and having a worl; rest freely rotatable on the top thereof, a gear resting on the top of the standard and having a passage therethrough for the smaller screw, said gear and smaller screw being` splined together so as to permit longitudinal motion of the screw and pre-vent relative rotation of the screw and gear, whereby when the gear is turned the hollow screw will act as a stationary nut-to cause the inner screw to rise as it turns, said inner screw having means at the bottom thereot for preventing its screwing out oie its nut, whereby when said means comes into action the two screws will turn together with gear and the outer screw will move upwardly, taking the trame with it.

el. ln a jack, the combination with a standard screw-threaded internally, ot a screw operating in said screw thread and having a passage therethrough also threaded, an inner screw threaded in said passage, means 'for operating the inner screw, and means at the bottomof the inner screw `for engaging the bottom of the inner thread on the outer screw when the inner screw rises to its limiting position, whereby -from that time on the outer screw and inner screw will turn together and both rise in accordance with the thread on the out-side of the outer screw.

In testimony whereof we have hereunto atlixed our signatures.

ALVIN L. JOHNSON. WATERMAN GOULDING WARREN. 

